1. Field of the Invention
The present invention relates to electromechanical actuators of the type having a flat armature positioned to move in a magnetic gap, and more particularly to such actuators wherein the armature comprises a conductive pattern formed on a sheet of insulating material.
2. Discussion Relating to the Problem
Compact low-cost electromechanical actuators such as DC motors are employed in a wide variety of consumer products from toys to tape recorders and cameras. In many such applications, to take best advantage of available space in the apparatus, a thin, flat actuator is desirable since the thin, flat spaces are more readily available than bulky, cubic or prismatic volumes. To this end, it is known to employ an electromagnetic actuator having a thin, flat armature which resides for movement in a magnetic gap. U.S. Pat. No. 3,993,920 issued Nov. 23, 1976 to Sato, shows a flat, circular motor useful for example, in a tape recorder.
One embodiment of the motor, called a pancake motor, comprises a housing and a flat permanent stator magnet forming an annular magnetic gap between the magnet and one side of the housing. A thin, flat, circular armature comprises a printed circuit coil photofabricated on a thin, stiff sheet of insulating material having a central axle perpendicular to the plane of the armature. The armature is supported in the magnetic gap of the motor by a pair of bearings. Another embodiment of the motor, commonly called a cup or basket motor, comprises a cylindrical housing and a cylindrical permanent magnet forming a cylindrical magnetic gap between the magnet and the side of the housing. A thin cylindrical armature comprises a printed circuit coil photofabricated on a thin, stiff sheet of insulating material and formed into a cylinder. The armature has a central axle along the axis of the the cylinder. The armature is supported in the magnetic gap by a pair of bearings.
An improved actuator of the type described above is disclosed in U.S. Pat. No. 4,413,895 issued Nov. 8, 1983 to J. K. Lee, the improvement therein comprises making the armature very thin and compliant so that the armature is supported in the magnetic gap by the surfaces defining the gap. This feature minimizes friction problems associated with the armature coming into contact with the sides of the gap while maintaining a minimum sized gap for maximum power output of the actuator. In one embodiment disclosed in the application, a first compliant armature/actuator is employed to control a shutter in a camera, and a second compliant armature/actuator is employed to control the focus of a lens in the camera. The two actuators are integrated on a common mechanism plate that serves as a flux return path for the magnets associated with both actuators. Although such actuators are relatively compact, the use of a plurality of actuators to control a number of functions in the camera increases the weight and size of the camera control mechanism in proportion to the number of actuators employed. The present inventors were faced with the problem of controlling a number of functions with electromechanical actuators while minimizing the weight and size of the actuators employed.